Recently, there are vigorous movements to push forward energy saving as measures against warming, a global environmental issue. As for apparatuses using hot/cold heat, a heat insulating material having an excellent heat insulation capability is demanded in the viewpoint of effective utilization of heat. Particularly, where a heat insulating material is used in an elevated-temperature range of exceeding 150° C., energy-saving effects appear conspicuously. Applications are expected for printers, copiers, liquid-crystal projectors and semiconductor manufacturing apparatuses.
In the high-temperature range of exceeding 150° C., because the radiation-heat conduction component due to infrared rays (hereinafter, referred to as IR) is not ignorable differently from that in the room temperature range, the capability as the heat-insulating material decreases. This requires a technique to suppress against radiation heat conduction. Concerning the technique for suppressing radiation heat, there is disclosed in JP-A-5-164296 a heat-insulating film having a metal-foil layer and protection layer over a plastic film.
FIG. 8 is a sectional view of a heat-insulation film in the conventional art.
Heat-insulating film 1 is plastic film 3 having thereon surface layer 2 of a metal high in purity but coarse in crystal-grain size. Over planar surface of layer 2, metal thin layer 4 having a small thermal emissivity is layered in a manner having extremely-flattened crystal grains. Over a surface of metal thin layer 4, protection layer 5 is formed for covering metal thin layer 4 in a manner stably keeping its surface while allowing IR and far-infrared rays (hereinafter, referred to as FIR) to transmit freely.
The heat rays, of IR and FIR intruding heat-insulating film 1, are to repeat total reflections within metal thin layer 4 having extremely-flat crystal grains and then reflect toward the outside, thus obtaining high heat-insulating effects.
However, the above structure does not disclose how to join the metal thin layer and the protection layer together, hence being impractical. Should an adhesive be used, IR and FIR are to be absorbed in the adhesive, to raise a problem of reducing the IR reflection effect.
Meanwhile, JP-A-5-193668 discloses a heat-insulating lamination film having an IR reflectiveness, as an envelope material for a vacuum heat insulating material.
FIG. 9 is a sectional view of a heat insulating lamination film in the conventional art. The heat-insulating lamination film has protection layer 5, FIR-reflection layer 6, gas-barrier layer 7 and thermal bonding layer 8 that are bonded together by an adhesive 9A. The heat-insulating lamination film can obtain a high FIR reflectivity because of using an FIR transmissive substance for protection layer 5 and a metal foil for FIR-reflection layer 6.
Furthermore, because of using the FIR transmissive substance in protection layer 5, IR is allowed to reach FIR-reflection layer 6.
However, the IR transmissive substance is indefinitely defined wherein the adhesive 9A of between protection layer 5 and FIR-reflection layer 6 is indefinite because there is defined nothing but such an adhesive as not to lose the FIR transmission effect.
The present invention is for solving the conventional problems, and it is an object thereof to provide a film having an excellent IR reflection effect for suppressing conduction of radiation heat.
In the meanwhile, in the temperature range of from −30 to 100° C. or around, it is a practice to use, as a general heat-insulating material, a fibrous substance such as glass wool or a foamed substance such as urethane foam. In the applications requiring a heat-insulating material higher in capability, there is means applied with a vacuum heat-insulating material structured by covering a core material holding a space of fine gaps with an envelope material shielding against external-air intrusion, to thereby reduce the pressure in the space thereof.
A vessel thermally fused of metal or the like can be used for the envelope material of a vacuum heat-insulating material. However, in the low-temperature range not requiring heat resistance, it is a frequent practice to use a plastic-metal lamination film, having a thermal bonding layer, a gas-barrier layer and a protection layer, that is comparatively to be bent or curved.
Recently, the requirement for the vacuum heat-insulating material is in a tendency toward a diversification. Thus, demand is for a further higher capability of vacuum heat-insulating material.
Meanwhile, in the office appliances such as computers, character printers and copiers and fluorescent lamps incorporating inverters, etc., there is a strong demand for a high-capability heat-insulating material that can be used at around 150° C. in order not to convey the heat caused from a heat-generating member arranged in the main body to a toner less resistive to heat or an interior precise component.
There are inorganic fibrous materials, such as glass wool, and inorganic foamed substance as usual heat-insulating materials, that are to be used in a temperature range at around 150° C. However, there is a strong demand for a higher-capability heat-insulating material. In this temperature range, it is possible to apply only those of vacuum heat-insulating materials that are under especial high-temperature specifications, due to the reliability of lamination films thereof.
Heat conduction, generally, is represented in terms of the sum over in-gas heat conduction, in-solid heat conduction, radiation heat conduction and convectional heat conduction. At around normal temperature, in-gas and in-solid heat conductions are predominant wherein radiation heat conduction is less to contribute.
However, radiation heat conduction gradually increases with increasing temperature. At 100° C. and higher, the effect of heat conduction due to radiation heat becomes no longer ignorable. In the further higher temperature range, radiation heat conduction becomes predominant. Accordingly, at 150° C. or the around, there is a need of a heat-insulating material specification taking account of reduced radiation heat conduction.
Conventionally, there are a number of reports of arts to suppress against radiation heat by means of IR-reflective metal surfaces, IR-reflective paints and so on. Because of experiencing IR radiation energy over a long term, the metal surface problematically deteriorates due to its surface oxidation. The IR-reflective paints are not sufficient in their IR reflectivities. For this reason, a JP-A-2001-107480 discloses, as a heat-shield sheet, a sheet that a flexible sheet member, at its one or both surfaces, is formed with a heat-reflective paint layer having a resin paint mixed therein with a ceramic or inorganic compound having a heat reflectiveness, to interpose a metal foil between the heat-reflective paint layer and the sheet member.
FIG. 17 is a cross-sectional view of the heat-shield sheet in the conventional art. Heat-shield sheet 20 is structured by bonding aluminum foils on both surfaces of sheet member 22 to thereby form upper reflective film 23A and lower reflective film 23B and forming, by application, heat-reflective paint layers 24A, 24B on exposure surfaces of the aluminum foils. In using the heat-reflective paint layers of heat-shield sheet 20 directed toward a heat source such as solar light, the aluminum foil at its film has a high reflectivity of IR radiation energy, hence being allowed to efficiently reflect emission energy. This is considered to conspicuously improve heat-shield capability. However, in the above structure, there is a difficulty in obtaining a sufficient heat-shield effect despite using the IR-reflective metal foils and the reflective paint layers together. This is because the incident IR first is partly reflected by the IR reflective paint layer but the major part thereof is absorbed therein and conducted by in-solid heat conduction into the adjacent metal foil. The IR does not reach the metal foil and the metal foil does not exhibit its IR reflectiveness. As a result, the major part of radiation heat is converted into in-solid heat conduction, thus being conducted.
Meanwhile, Japanese Utility Model No. 3,085,643 discloses a heat-insulation tape that a paint-type heat-insulating material is applied under high pressure onto a surface of a metal-foil tape and a strong hear-resistive adhesive is applied onto a backside thereof, to be wound in a roll form by sandwiching an adhesion-preventive paper tape thereon.
However, in also the conventional-art structure, the paint-type heat-insulating material on the surface of the metal-foil tape absorbs the greater part of IR, thus making it difficult to obtain a sufficient heat-shield effect.
The invention is for solving the conventional problem, and it is an object thereof to provide a radiation-heat suppression film that sustains the IR reflecting capability over a long term and exhibits an excellent radiation-heat suppression.
Meanwhile, as for capability improvement of the vacuum heat-insulating material, for suppressing influence of radiation to obtain high heat-insulation capability, JP-A-5-193668 discloses a heat-insulating lamination film as an envelope material made up with a protection layer, an FIR reflection layer, a gas-barrier layer formed by a metal foil, and a thermal bonding layer, wherein the protection layer uses an FIR-transmissive substance.
Where PET, in general use, is formed into a protection layer, the incident IR reflects in part thereof but the greater part thereof is absorbed in the protection layer and conduced by in-solid heat conduction to the adjacent gas-barrier layer.
In the above conventional art structure, the incident IR transmits through the protection layer, of an FIR-transmissive substance, and then reflects upon the gas-barrier layer. As a result, it serves as a vacuum heat-insulating material capable of suppressing against radiation-heat conduction. In this manner, there is described to provide a vacuum heat-insulating material suppressing against in-gas and radiation heat conductions and having an excellent heat-insulation capability.
There is no especial definition of the FIR-transmissive substance herein, wherein a methylpentene polymer film is described effective.
However, in the conventional art structure, the FIR-transmissive substance and the FIR-reflection are indefinitely defined. Radiation heat conducts by absorbing, principally, 2-25 μm of IR and again emitting it.
As shown in FIG. 26, the wavelength distribution of radiation heat changes depending upon the temperature of a heat-generation source, wherein the peak shifts to the lower wavelength as the temperature is higher.
It can be seen that the radiation-heat emission spectrum, at 150° C., has a peak wavelength at or around 7 μm, having a form having a shoulder somewhat closer to the higher wavelength. It can therefore be considered that the radiation-heat conduction at 150° C. can be suppressed by impeding the IR absorption in the vicinity of 4-20 μm. Namely, it is of importance to define an IR-transmissive substance and IR-reflective substance in the range of 4-20 μm.
It is an object of the present invention to provide a vacuum heat-insulating material that is to sustain an IR-reflective capability over a long term and exhibit an excellent radiation-heat-conduction suppressivity. It is another object to provide a vacuum heat-insulating material that can be used in a high-temperature range where application is conventionally difficult to implement, by providing a radiation-heat-conduction suppressivity.